Marine Geophysics and Hydroacoustics

NW Africa

The passive margin off NW-Africa is investigated by the workgroup since a long time; it is shaped by a complex interplay of sediment transport processes, directed both downslope and alongslope. During several cruises, sediment transport processes between 12° and 29°N off Senegal, Mauritania, and Western Sahara were investigated by means of geophysical and sedimentological methods. More... Sediment transport on the Northwest African continental margin operates with different rates and styles: some sections of the margin show a large concentration of upper slope canyons but no indication for significant mass wasting, whereas other sections are characterized by large-scale mass wasting with no canyons or gullies. Four mega-slides, each affecting over 20,000 km2 of seafloor, have been identified along the continental slope off Northwest Africa. All slides are complex in morphology and show a stepped headwall pattern typical for retrogressive failure. Several buried mass transport deposits are seismically imaged beneath all near-surface slides indicating a long history of mass wasting for some sections of the margin.

The most recent cruise (RV Merian Cruise MSM32, 25.09.-30.10.2013) investigated the Agadir Canyon region.

Ausbringen des tiefgeschleppten Sidescan Sonars TOBI.

Deployment of the deep-towed sidescan sonar operated by NOCS.

Agadir Canyon is one of the largest submarine canyons in the world, supplying giant submarine sediment gravity flows to the Agadir Basin and the wider Moroccan Turbidite System. While the Moroccan Turbidite System is extremely well investigated, almost no data from the source region, i.e. the Agadir Canyon, are available. Understanding why some submarine landslides remain as coherent blocks of sediment throughout their passage downslope, while others mix and disintegrate almost immediately after initial failure, is a major scientific challenge, which was addressed in the Agadir Canyon source region during Cruise MSM32. We collected ~ 1500 km of seismic 2D-lines in combination with a dense net of hydroacoustic data. About 1000 km2 of sea floor were imaged during three deployments of TOBI (deep-towed sidescan sonar operated by the National Oceanography Centre Southampton). A total of 186 m of gravity cores and several giant box cores were recovered at more than 50 stations. CTD casts were collected at nine stations including one 13 hour Yo-yo CTD. The new data show that Agadir canyon is the source area of the world’s largest submarine sediment flow, which occurred about 60,000 years ago. Up to 160 km3 of sediment was transported to the deep ocean in a single catastrophic event. For the first time, sediment flows of this scale have been tracked along their entire flow pathway. A major landslide area was identified south of Agadir Canyon. Landslide material enters Agadir canyon in about 2500 m water depth; the material is transported as debrite for at least another 200 km down the canyon. Initial data suggest that the last major slide from this source entered Agadir canyon at least 130,000 years ago. Living deep-water corals were recovered from a large mound field north of Agadir canyon. To our knowledge, these are the first living cold water corals recovered off the coast of Morocco (except for the Gulf of Cadiz). They represent an important link between the known cold-water coral provinces off Mauritania and in the Gulf of Cádiz.

Bathymetrie des Agadir-Canyons

Bathymetry of Agadir Canyon, recorded during cruise MSM32.

 

Contact for this project:  Sebastian Krastel

Most relevant publications:

  • Li W., Alves, T.M., Urlaub, M., Georgiopoulou, A., Klaucke, I., Wynn, R.B., Gross, F., Meyer, M., Repschläger, J., Berndt, C., Krastel, S. (accepted for publication in Marine Geology) Morphology, age and sediment dynamics of the upper headwall of the Sahara Slide Complex, Northwest Africa: Evidence for a large late Holocene failure
  • Krastel, S., Wynn, R.B., Feldens, P., Schürer, A., Böttner, C., Stevenson, C., Cartigny, M., Hühnerbach, V., Unverricht, D. (2016) Flow behaviour of a giant landslide and debris flow entering Agadir Canyon, NW Africa. In: Submarine mass movements and their consequences (eds: Lamarche, G. et al). Advances in Natural and Technological Hazards Research, 41, Springer, 145-154.
  • Glogowski, S., Dullo, W.-C., Feldens, P., Liebetrau, V., von Reumont, J., Hühnerbach, V., Krastel, S., Wynn, R.B., Flögel, S. (2015) The Eugen Seibold coral mounds offshore western Morocco: oceanographic and bathymetric boundary conditions of a newly discovered cold-water coral province. Geo-Marine Letters, 25, 257-269, DOI: 10.1007/s00367-015-0405-7
  • Krastel, S., Lehr, J., Winkelmann, D., Schwenk, T., Preu, B., Strasser, M., Wynn, R.B., Georgiopoulou, A., Hanebuth, T. (2014) Mass wasting along Atlantic continental margins: a comparison between NW-Africa and the de la Plata River region (northern Argentina and Uruguay). In: Submarine mass movements and their consequences (eds: Krastel et al). Advances in Natural and Technological Hazards Research, 37, 459-469.
  • Krastel, S., Wynn, R.B., Georgiopoulou, A., Geersen, J., Henrich, R., Meyer, M., Schwenk, T. (2012) Large scale mass wasting at the NW-African Continental Margin: some general implications for mass wasting at passive continental margins. Submarine mass movements and their consequences. In: Yamada, Y. et al. (eds), Advances in Natural and Technological Hazards Research, 31, Springer, 189-199.
  • Meyer, M., Geersen, J., Krastel, S., Schwenk, T., Winkelmann, D. (2012) Dakar Slide offshore Senegal, NW-Africa: Interaction of stacked giant mass-wasting events and canyon evolution. Submarine mass movements and their consequences. In: Yamada, Y. et al. (eds), Advances in Natural and Technological Hazards Research, 31, Springer, 177-188.
  • Pierau, R., Henrich, R., Preiß-Daimler, I., Krastel, S., Geersen, J. (2011) Sediment transport and turbidite architecture in the submarine Dakar Canyon off Senegal, NW-Africa. Journal of African Earth Sciences, 60, 196-208.
  • Georgiopoulou, A., Masson, D., Wynn, R.B., Krastel, S. (2010) The Sahara Slide: Initiation and processes from headwall to deposit of a giant submarine slide. G-cubed. 11-7. doi:10.1029/2010GC003066.

 

Übersicht der Rutschungen vor der Küste NW-Afrikas.

Overview of submarine landslides offshore NW Africa.

 

Ausbringen des Streamers für die Seismik an Bord des FS Maria S. Merian.
Deployment of the streamer for seimics aboard of RV Maria S. Merian.
 
Sedimentproben und -kerne werden aus dem Großkastengreifer genommen.
Sediment cores are taken from the box corer.
 
Schwerlot an Bord des FS Maria S. Merian.
Gravity corer aboard of RV Maria S. Merian.